This invention relates to a cylinder head and valve train arrangement for a multiple valve engine and more particularly to an arrangement for improving the performance of an engine through the use of multiple valves and permitting a simple and highly effective construction to achieve this result.
It has been basically understood that the performance of an internal combustion engine can be improved by improving the breathing of the intake charge into the combustion chamber and the exhaust charge from the combustion chamber. It is also well known that the breathing and volumetric efficiency of an engine can be improved by increasing the number of valves rather than merely providing a single extremely large intake valve and a single extremely large exhaust valve. By using multiple smaller valves, the inertia can be reduced and higher engine speeds obtained. However, there still is a significant problem in placing all of the components within the combustion chamber and also insuring that the combustion chamber has a proper configuration.
In high performance engines at the present time, four valves per cylinder are now becoming increasingly common. Such arrangements all employ two intake valves and two exhaust valves per chamber. It has been proposed also to employ arrangements with five valves (three intake and two exhaust) so as to permit even further increases in performance. Although it was thought that five valves per cylinder might be the optimum number, considering the problems in connection with valve placement and valve actuation, it is now believed that the provision of six valves (four intake and two exhaust) can offer still further performance increases. However, there are a wide variety of problems in connection with the provision of so many valves in a single combustion chamber.
It is, therefore, a principal object of this invention to provide an improved cylinder head arrangement for an internal combustion engine employing six valves for each cylinder.
It is a further object of this invention to provide an improved cylinder head arrangement that employs four intake valves and two exhaust valves per cylinder.
One problem attendant with the provision of a large number of valves for the engine is the porting arrangement for the individual valves. If individual ports are provided for each valve, then the cylinder head configuration becomes extremely complicated. On the other hand, if the valves are siamese so that a plurality of valves are served by a common port, this can give rise to flow irregularities through the individual valves and less than adequate utilization of the valve area.
It is, therefore, a still further object of this invention to provide an improved multiple valve arrangement for an internal combustion engine having siamese porting and insuring equal flow through all of the valves.
It is a further object of this invention to provide an improved porting arrangement for a multiple valve engine wherein a single port serves all valves and wherein the flow through all of the valves will be equal.
In connection with the use of multiple valves for an engine, it is also desirable to use light alloy materials for the cylinder head. However, when light alloy cylinder head materials are employed, it is the practice to use some form of valve seat insert for actually forming the seating surface of the valve. Such inserts are normally pressed in or inserted into the cylinder head material in some similar manner. However, when multiple valves are employed, the cylinder head surface may not be able to accept such a wide number of inserts.
It is, therefore, a still further object of this invention to provide an improved valve arrangement for an engine wherein a single insert forms a plurality of valve seats.
In connection with the utilization of multiple valves, it is, of course, desirable to minimize the number of camshafts employed for operating all of the valves. Generally, it has been the practice with four and five valve per cylinder engines to employ two camshafts, one for operating the intake valves and one for operating the exhaust valves. However, when one camshaft is called upon to operate more than three valves, then the placement of the valves can be compromised. Specifically, if there are four valves per cylinder operated by a single camshaft, it is normally the practice to align the valves so that they all reciprocate along axes that lie in a plane that will intersect or pass near the rotational center of the camshaft axis. This means that the actual length of the camshaft and specifically the lobes require the valves to be all positioned so that the combustion chamber configuration tends to be large and provide large surface areas. This obviously reduces the possible compression ratio of the engine and, accordingly, its performance.
It is, therefore, a still further object of this invention to provide an improved arrangement for operating multiple valves from a single camshaft and wherein the valves can reciprocate about axes that are not within a common plane so as to facilitate improved combustion chamber configuration.
It is a further object of this invention to provide an improved camshaft operating arrangement for an engine wherein the valve placement and camshaft construction is such that the combustion chamber configuration need not be compromised and yet a single camshaft can be employed to operate multiple valves.
In conjunction with the use of a single camshaft for operating multiple valves, it is frequently the practice to employ separate cam lobes for operating each individual valve or groups of valves. However, where there are multiple valves and the use of multiple cam lobes, then the rotational support for the camshaft presents some problem. That is, the highest axial loading on the camshaft occurs in the area of the cam lobes where they engage the valve actuating elements. However, if the cam lobes are all placed close to each other, it is difficult if not impossible to provide a bearing surface adjacent the cam lobes in order to take these side loadings. Conventional camshaft arrangements simply do not afford the opportunity to provide adequate bearing surfaces for the camshafts under these circumstances.
It is, therefore, a further object of this invention to provide a camshaft arrangement for a multiple valve engine wherein the cam lobes can be spaced widely enough apart so as to afford adequate bearing surface.
It is a further object of this invention to provide an improved bearing arrangement for a multiple valve actuating camshaft for an engine.
In some instances with multiple valve engines, it may be desirable to employ more than two camshafts for driving all of the valves of the engine. Where such an arrangement is employed, however, then it becomes important to insure that all of the camshafts are driven in the same timing relative to the engine output shaft. However, the timing drive should be relatively simple, uncomplicated and afford ready access to the components of the engine.
It is, therefore, a further object of this invention to provide an improved camshaft drive arrangement for driving at least three camshafts from the engine output shaft.